[0001] This invention relates to lactacystin derivatives, which are derived from lactacystin
produced by a microorganism strain Streptomyces sp. OM-6519 belonging to genus Streptomyces
with inducing outgrowth of neurites. The compounds induce outgrowth of neurite, with
low cytotoxicity and high selective toxicity and are useful for pharmaceuticals.
[0002] It has been known that lactacystin of the formula

having neuritogenesis activity was produced by culturing physiologically active substance
OM-6519 producing microorganism belonging to genus Streptomyces and isolating the
compound hereinabove. (J. Antibiotics. 19: 44, 113-116 and Japan. Pat. Unexam. Publ.,
No 3-98594).
[0003] Nagamitsu, J. Antibiotics (1995) Vol. 48,7,747-748, Fenteany
et al, Science (1995) vol 268,726-731, and Fenteany
et al, Proc. Natl. Acad. Sci (1994) Vol. 91, 3358-3362, all describe lactacystin or lactacystin
derivatives and the activity of those compounds. Corey
et al, Tetrahedron letters 1993 Vol. 34, 44, 6977-6980, Corey
et al, Tetrahedron letters 1993 Vol. 34, 44, 6973-6976, and Corey
et al, Tetrahedron letters 1993 Vol. 34, 44, 6969-6972, describe synthesis of lactacystin.
[0004] Lactacystin has the property of specifically inducing activity of outgrowth of neurite,
however it is highly cytotoxic and shows no selective toxicity. Accordingly, lactacystin
derivatives with superior inducing activity of neuritogenesis and high selective cytotoxicity
have been desired to find out.
[0005] We have sought to solve the above problems and found that lactacystin derivatives
of the formula (1) hereinbelow showed superior inducing activity of neuritogenesis
and high selective toxicity to the known lactacystin.
[0006] The present invention provides a lactacystin derivative of the formula

wherein R is branched or unbranched C
1-C
4 alkyl, and
n is 0 to 4, or a pharmacologically acceptable salt thereof.
[0007] Examples of alkyl are methyl, ethyl, propyl, isopropyl, butyl, isobutyl, s-butyl
and t-butyl. Preferable examples are methyl, ethyl, propyl and isopropyl.
[0008] A derivative of formula(1) can be produced by reacting β-lactone (2) of the formula
(2):

with a mercapto compound of the formula
HS-(CH
2)
nR
wherein n and R are as defined above, in the presence of a tertiary organic amine
in an inert organic solvent.
[0009] Examples of the inert organic solvent used in the above reaction are dichloromethane,
chloroform and tetrahydrofuran. Examples of the tertiary organic amine used in the
above reaction are known tertiary organic amines. Preferred examples are trimethylamine
and triethylamine.
[0010] Preferred examples of the mercapto compound are, for example, ethane thiol, propane
thiol, isopropane thiol, butane thiol, 1-methyl-1-propane thiol and 1-pentane thiol.
[0011] The above reaction proceeds preferably under inert gas such as argon and nitrogen
gas. The reaction proceeds at room temperature. Reaction can be traced by TLC and
HPLC, and is terminated by maximum production of the desired derivative.
[0012] Isolation of the derivative can be performed by removing solvent from the reaction
mixture and treating the residue with column chromatography.
[0013] The thus obtained derivative (1) can be further purified by means of conventional
means for isolation and purification of organic compounds, for example combination
of extraction, crystallization and chromatography.
[0014] Pharmacologically acceptable salts of the derivative (1) can be prepared by conventional
methods for preparation of the salt.
[0015] Examples of the derivatives of the present invention or comparison compounds are
as follows:
3-hydroxy-2-(1-hydroxy-2-methylpropyl)-4-methyl-5-oxo-2-pyrrolidine-ethanethiocarboxylate
(1)
R: CH3, n = 1
3-hydroxy-2-(1-hydroxy-2-methylpropyl)-4-methyl-5-oxo-2-pyrrolidine-propanethiocarboxylate
(2)
R: CH3, n=2
3-hydroxy-2-(1-hydroxy-2-methylpropyl)-4-methyl-5-oxo-2-pyrrolidine-iso-propanethiocarboxylate
(3)
R: -CH(CH3)2, n = 0
3-hydroxy-2-(1-hydroxy-2-methylpropyl)-4-methyl-5-oxo-2-pyrrolidine-butanethiocarboxylate
(4)
R: -(CH2)3CH3, n = 0
3-hydroxy-2-(1-hydroxy-2-methylpropyl)-4-methyl-5-oxo-2-pyrrolidine-1-methyl-1-propanethiocarboxylate
(5)
R: -CH2CH(CH3)2, n = 0
3-hydroxy-2-(1-hydroxy-2-methylpropyl)-4-methyl-5-oxo-2-pyrrolidine-1-pentanethiocarboxylate
(6)
R : CH3, n = 4
[0016] Pharmacological activity of the derivative (1) and its pharmacologically acceptable
salt are explained hereinbelow.
1. Activity of neuritogenesis and cytotoxic action:
(1) Test method:
[0017] Morphological changes of Neuro 2A cells are obseved according to the method of Baglioni
et al. [J. Biol Chem., 266: 18620 (1991)].
[0018] Neuro 2A cells were plated at a density of 1 × 10
4 cells/cm
2 in a 24 hole plate, and cultured in MEM-H with 10% FBS. On the next day, lactacystin
or lactacystin derivatives were added at the concentration of 0.05 - 100 µM, and morphological
changes of the cells were observed time dependently by- phase contrast microscope.
[0019] Minimum effective dose of the substances was defined as a concentration in which
approximately 20% of whole cells showed induction of bipolar outgrowth of neurite.
[0020] Cytotoxicity of the compounds is defined when no attached Neuro 2A cells were observed
at above 2/3 of the whole cells.
(2) Results:
[0021] Results of the tests are shown in Table 1.
2. No specific test method for selective toxicity of the compounds is known, therefore
the selective toxicity is defined as a ratio of cytotoxicity/minimum effective dose.
[0022] Result is shown in Table 1.
Table 1
| Compound (Example No.) |
Minimum effective dose (µM) (A) |
Cytotoxicity (µM)(B) |
Selective toxicity (B/A) |
| 1 |
0.20 |
1.56 |
8 |
| 2 |
0.20 |
3.12 |
16 |
| 3 |
0.40 |
12.5 |
31 |
| 4 |
0.40 |
12.5 |
31 |
| 5 |
0.40 |
12.5 |
31 |
| 6 |
0.80 |
12.5 |
16 |
[0023] As shown in Table 1, the derivative (1) or pharmacologically acceptable salt thereof
of the present invention is superior inducing activity of outgrowth of neurite to
the known lactacystin with higher selective toxicity on the cells. Therefore novel
effective lactacystin derivatives are provided.
[0024] The compounds of the present invention, as well as lactacystin, are the neurotrophic
factor, and induce neuritogenesis and cause a transient increase in the intracellular
cAMP level in mouse neuroblastoma cell line Neuro 2A. Therefore the lactacystin derivatives
and salts thereof of the present invention can be used in the treatment of dementia.
Accordingly the compounds of the present invention can be applied as a neurotrophic
drug. The dosage is usually approximately 200 mg/man i.v. When the compounds of the
present invention are administered in doses of 100 mg/kg i.p. in mice, no deaths are
observed.
[0025] Following examples and referential examples illustrate the invention.
Referential example 1
[0026] Lactacystin (45.5 mg) dissolved in ethanol (0.31 ml) and 0.1 N sodium hydroxide (0.93
ml) was stirred at room temperature for 30 minutes. Reaction mixture was neutralized
with addition of 2N HCl and dried in vacuo. Residue was purified by preparative TLC
(developer, THF : H
2 O = 10 : 1) to obtain γ-lactam 26.2 mg (yield : 94.0%).
1H-NMR (270 MHz, CD
3 OD) δ 0.85 (d, J = 6.6 Hz, 3H, (CH
3)
2CH), 0.8 6 (d, J = 6.6 Hz, 3H, (CH
3)
2CH), 0.98 (d, J = 7.6 Hz, 3H, HOCHCHCH
3), 1.69 (m, 1H, (CH
3)
2CH), 2.86 (m, 1H, HOCHCHCH
3), 3.83 (d, J = 5.3 Hz, 1H, HOCH), 4.30 (d, J = 5.9 Hz, 1H, HOCHCHCH
3)
LRMS (FAB, Glycerol matrix) m/z 232 [(M+H)
+ ; calcd for C
10H
18NO
5 : 232]
Referential example 2
[0027] γ-lactam (43.3 mg, 0.187 mmol) was dissolved in dichloromethane (0.7 ml) under argon
atmosphere. BOPCl (1.5 eq., 0.305 mmol. 77.6 mg) and triethylamine (3 eq., 0.609 mmol,
85µl) were added thereto. Reaction mixture was stirred at room temperature for 70
minutes. cooled to 0°C and added water therein to stop the reaction. The reaction
mixture was transferred into separating funnel, extracted with chloroform and dried
by adding Na
2SO
4. The extract was concentrated in vacuo and purified using silica gel column chromatography
(extracting solvent; CHCl
3 : MeOH = 50 : 1) to obtain β-lactone 27.2 mg (yield : 68.0%).
1H-NMR (270 MHz , CD
3Cl
3) δ 0.84 (d, J = 6.8 Hz, 3H, (CH
3)
2 CH), 0.99 (d, J = 6.8 Hz, 3H, (OH
3)
2CH), 1.27 (d, J = 7.6 Hz, 3H, CH
3CHCHOH), 1.8 2 (m, 1H, (CH
3)
2CH), 2.69 (m, 1H, CH
3CHCHOH), 3.91 (d, J = 6.9 Hz, 1H, HOCHCH), 5.15 (d, J = 6.3 Hz, 1H, CH
3CHCHOH), 6.25 (s, 1H, NH)
13 C-NMR (67.5 MHz, CDCl
3 δ 8.1, 16.3, 20.0, 29.6, 38.1, 64.0, 71.8, 76.0, 171.1, 176.8
LRMS (FAB, NBA matrix) m/z 214 [(M+H)
+ ; calcd for C
10H
16NO
4 : 14]
Example 1
[0028] β-lactone (10 mg, 0.047 mmol) obtained in the method of referential example 2 was
dissolved in dichloromethane (1.0 ml) under argon atmosphere. Triethylamine (6 eq.,
0.0282 mmol, 39.3µl) and ethanethiol (3 eq., 0.141 mmol. 10.4µl) were added thereto.
Reaction mixture was stirred at 40 °C for 1 hour, concentrated in vacuo and purified
using preparative TLC (developer; CHCl
3 : MeOH = 10 : 1) to obtain 3-hydroxy-2-(1-hydroxy-2-methylpropyl)-4-methyl-5-oxo-2-pyrrolidine-ethanethiocarboxylate
10.3 mg (yield : 80%).
1H-NMR (270 MHz, CDCl
3) δ 0.79 (d, J = 6.6 H, 3H), 0.87 (d, J = 6.6 Hz, 3H), 0.9 8 (d, J = 7.6 Hz, 3H),
1.0 5 (t, J = 8.5 Hz - 3H), 1.58 (m, 1H), 2.25 (q, J = 8.5 Hz, 2H), 2.83 (m, 1H),
3.86 (d, J = 6.9 Hz, 1H), 4.43 (d, J = 6.6 Hz, 1H)
LRMS (FAB, NBA matrix) m/z 276 [(M+H)
+; calcd for C
12H
22NO
4S : 276]
Example 2
[0029] β-lactone (10 mg, 0.047 mmol) obtained in the method of referential example 2 was
dissolved in dichloromethane (1.0 ml) under argon atmosphere. Triethylamine (6 eq.,
0.0282 mmol, 39.3µl) and propanethiol (3 eq., 0.14 mmol, 14.5µl) were added thereto.
Reaction mixture was stirred at 40 °C for 1 hour, concentrated in vacuo and purified
using preparative TLC (developer: CHCl
3: MeOH = 10 : 1) to obtain 3-hydroxy-2-(1-hydroxy-2-methylpropyl)-4-methyl-5-oxo-2-pyrrolidine-propanethiocarboxylate
10.6 mg (yield : 78%).
1H-NMR (270 MHz, CDCl
3) δ 0.79 (d, J = 6.6 H, 3H), 0.87 (d, J = 6.6 Hz, 3H), 0.98 (d, J = 7.6 Hz, 3H), 1.05
(t, J = 8.5 Hz, 3H), 1.40 (m, 2H), 1.58 (m, 1H), 2.25 (q, J = 7.5 Hz, 2H), 2.83 (m,
1H) , 3.86 (d, J = 6.9 Hz, 1H), 4.43 (d, J = 6.6 Hz, 1H)
LRMS (FAB, NBA matrix) m/z 290 [(M+H)
+; calcd for C
13H
24NO
4S : 290]
Example 3
[0030] β-lactone (10 mg, 0.047 mmol) obtained in the method of referential example 2 was
dissolved in dichloromethane (1.0 ml) under argon atmosphere. Triethylamine (6 eq.,
0.0282 mmol, 39.3µl) and iso-propanethiol (3 eq., 0.141 mmol, 14.5 µl) were added
thereto. Reaction mixture was stirred at 60°C for 3 hours, concentrated in vacuo and
purified using preparative TLC (developer; CHCl
3 : MeOH = 10 : 1) to obtain 3-hydroxy-2-(1-hydroxy-2-methylpropyl)-4-methyl-5-oxo-2-pyrrolidine-iso-propanethiocarboxylate
8.8 mg (yield : 65%).
1H-NMR (270 MHz, CDCl
3) δ 0.79 (d, J = 6.6 H, 3H), 0.87 (d, J = 6.6 Hz, 3H), 0.98 (d, J = 7.6 Hz, 3H), 1.50
(d, J = 8.5 Hz, 6H), 1.58 (m, 1H), 2.53 (m, 1H), 2.83 (m, 1H), 3.86 (d, J = 6.9 Hz,
1H), 4.43 (d, 6.6 Hz, 1H)
LRMS (FAB, NBA matrix) m/z 290 [(M+H)
+ ; calcd for C
13H
24NO
4S : 290]
Example 4
[0031] β-lactone (10 mg, 0.047 mmol) obtained in the method of referential example 2 was
dissolved in dichloromethane (1.0 ml) under argon atmosphere. Triethylamine (6 eq.,
0.0282 mmol, 39.3µl) and butanethiol (3 eq., 0.14 mmol, 15.1 µl) were added thereto.
Reaction mixture was stirred at 60°C for 5 hours, concentrated in vacuo and purified
using preparative TLC (developer; CHCl
3 : MeOH = 10 : 1) to obtain 3-hydroxy-2-(1-hydroxy-2-methylpropyl)-4-methyl-5-oxo-2-pyrrolidine-butanethiocarboxylate
8.5 mg (yield : 62%).
1H-NMR (270 MHz, CDCl
3) δ 0.79 (d, J = 6.6 H, 3H), 0.87 (d, J = 6.6 Hz, 3H), 0.90 (t, J = 8.5 Hz, 3H), 0.98
(d, J = 7.6 Hz, 3H), 1.20 ∼ 1.30 (m, 4H), 1.30 (m, 2H), 1.58 (m, 1H), 2.25 (q, J =
8.5 Hz, 2H), 2.83 (m, 1H), 3.86 (d, J = 6.9Hz, 1H), 4.43 (d, J = 6.6 Hz, 1H)
LRMS (FAB, NBA matrix) m/z 304 [(M+H)
+; calcd C
14H
26NO
4 S : 304]
Example 5
[0032] β-lactone (10 mg, 0.047 mmol) obtained in the method of referential example 2 was
dissolved in dichloromethane (1.0ml) under argon atmosphere. Triethylamine (6 eq.,
0.0282 mmol, 39.3µl) and 1-methyl-1-propanethiol (3 eq., 0.141 mmol, 10.4µl) were
added thereto. Reaction mixture was stirred at 60°C for 15 hours, concentrated in
vacuo and purified using preparative TLC (developer; CHCl
3 : MeOH = 20 : 1) to obtain 3-hydroxy-2-(1-hydroxy-2-methylpropyl)-4-methyl-5-oxo-2-pyrrolidine-1-methyl-l-propanethiocarboxylate
7.8 mg (yield : 55%).
1H-NMR (270 MHz, CDCl
3) δ 0.79 (d, J = 6.6 H, 3H), 0.87 (d, J = 6.6 Hz, 3H), 0.98 (d, J=7. 6 Hz, 3H), 1.05
(d, J = 8.5 Hz, 6H), 1.40 (m, 1H), 1.58 (m, 1H), 2.25 (q, J = 8.5 Hz, 2H), 2.83 (m,
1H), 3.86 (d, J = 6.9 Hz, 1H), 4.43 (d, J = 6.6 Hz, 1H)
LRMS(FAB, NBA matrix) m/z 304 [(M+H)
+ ; calcd for C
14H
26NO
4S : 304]
Example 6
[0033] β-lactone (10 mg. 0.047 mmol) obtained in the method of referential example 2 was
dissolved in dichloromethane (1.0 ml) under argon atmosphere. Triethylamine (6 eq.,
0.0282 mmol. 39.3µl) and 1-pentanethiol (6 eq., 0.282 mmol, 35.0 µl) were added thereto.
Reaction mixture was stirred at 40°C for 6 hours, concentrated in vacuo and purified
using preparative TLC (developer; CHCl
3 : MeOH = 20 : 1) to obtain 3-hydroxy-2-(1-hydroxy-2-methylpropyl)-4-methyl-5-oxo-2-pyrrolidine-1-pentanethiocarboxylate
10.4 mg (yield : 70%).
1H-NMR (270 MHz, CDCl
3) δ 0.79 (d, J = 6.6 H, 3H), 0.80 (q, J = 8.5 Hz, 3H), 0.87 (d, J = 6.6 Hz, 3H), 0.98
(d, J = 7.6 Hz, 3H), 1.20 ∼ 1.40 (m, 6H), 1.58 (m, 1H), 2.25 (q, J = 8.5 Hz, 2H) 2.83
(m, 1H), 3.86 (d, J = 6.9 Hz, 1H), 4.43 (d, J = 6.6 Hz, 1H)
LRMS (FAB, NBA matrix) m/z 318 [(M+H)
+ ; calcd for C
15H
28NO
4S : 318]